Multiprotocol Label Switching (MPLS) is a new technology that combines OSI layer 2 switching technologies and OSI layer 3 routing technologies. The advantages of MPLS over other technologies include the flexible networking fabric that provides increased performance and scalability. This includes Internet traffic engineering aspects that include Quality of Service (QoS)/Class of Service (COS) and facilitate the use of Virtual Private Networks (VPNs).
The Internet Engineering Task Force (IETF) defines MPLS as a standards-based approach to applying label switching technology to large-scale networks. The IETF is defining MPLS in response to numerous interrelated problems that need immediate attention. These problems include, scaling IP networks to meet the growing demands of Internet traffic, enabling differentiated levels of IP-based services to be provisioned, merging disparate traffic types onto a single IP network, and improving operational efficiency in a competitive environment.
The key concept in MPLS is identifying and marking IP packets with labels and forwarding them to a modified switch or router, which then uses the labels to switch the packets through the network. The labels are created and assigned to IP packets based upon the information gathered from existing IP routing protocols.
The label stack is represented as a sequence of “label stack entries”. Each label stack entry is represented by 4 octets.
Label: Label Value, 20 bitsExp: Experimental Use, 3 bitsS: Bottom of Stack, 1 bitTTL: Time to Live, 8 bits
The label stack entries appear after the data link layer headers, but before any network layer headers. The top of the label stack appears earliest in the packet, and the bottom appears latest. The network layer packet immediately follows the label stack entry which has the S bit set.
Multi-protocol label switching (MPLS) networks are typically comprised of several packet-based switching systems interconnected by a variety of media (e.g., coaxial or fiber optic cable, unshielded twisted pair or even point-to-point microwave wireless) in a mesh-topology network similar to the public switched telephone network. In such a network, there might be several paths through the network between any two endpoints. MPLS networks carry data as packets wherein each packet includes a label on identifying a switched path through the network. The data label is appended to data packets so as to define a pathway through the network over which the data packets are to be routed.
A problem with any data network, including an MPLS network, is the amount of time required to recover from either a link failure or a switch failure. Empirical data shows that the time required to recover from a network failure can take several seconds to several minutes, an unacceptably long time. A method and apparatus by which the recovery time for a link or switch failure can be reduced to perhaps less than a few hundred milliseconds would be a significant improvement over the prior art fault recovery mechanisms used on MPLS networks to date. A method and apparatus by which a switch over from a working path to a protection path would facilitate MPLS network reliability.